Pilot valve



June 1, 1943. w. c. TRAUTMAN 2,320,763

PILOT VALVE Filed NOV. 29, 1941 l RESERVOIR ACCUMULATOR 26 OLIE- pmolVALVE 278 372 TO HYDRAULIC 30 i SYSTEM f www 24 22 2o l2 34 48CHEC'K'VALVE 43\ `le |4 46\ I PUMP )66 44'\\ le 19 4|\ I 42\ I I9 I A'FIG, I 34 POWER VALVE se I 76 re 60 74E PRESSURE 702- M -52 7o' Bgzx*CYLINDER l v1lv 75, gg 5 `5$450 75 i z FIG. 2 mwr /5664 g ff cHAusT 84 lO34 4 FIG. 3

Y |O4." i?, Y \PLAsTIc 'Ozl y INVENTQR. 3 9 /j WALTER C. TRAUTMAIXI l BYff .O6 #wmmf voir III.

l Patented June 1, 1943 Walter C. Trautman, North Hollywood, alif.;assignor, by mesne assignments',v togBendix` Aviation, Ltd., NorthHollywood, Calif., a corporation of California Application November29,1941,seria1N0.420,915

4 claims. (011277-415 '1 This invention relates to pilot valves and moreparticularly toa pilot valve ofthe poppet valve v type.

It is an object of the invention to provide a satisfactory pressureresponsive `pilotrvalve element for use in iiuid pressure systems. i

It is another object of the invention to provide a pilot valve elementhaving no leakage, and having extreme accuracy of performance in regardto the fluid pressure at winch it is actuated.

AStill another object is to provide a pilot valve element having itsmovingparts co-axially `arranged for ease in machining and manufacture.

Another object is to provide an adjustable pressure responsive pilotvalve which may be readily adjusted to operate at difl'erent pressures.

In the drawing forming a part of this specication:

Figure l is a diagram of a hydraulic system showing the pilot valve ofthis'invention and showing its relation to the various unitsfin ahydraulic system; f

Figure 21s a view in vertical section of the pilot valve element ofFigurel; and

Figure 3 is an elevation view partly'in section of an alternative doublepoppet construction for the valve of Figurez.

Referring to Figure l, hydraulic lfluid is stored at atmosphericpressure in a reservoir I0, having aconduit I2 leading therefrom andconnected to a power operated pump I4. The pump `I4 delivers its outputto a conduit I6 connected to'a valve l housing I8. Leading from valvehousing I6 is an exhaust conduit I9` connected to the reser- A branchconduit leading fromconduit'l is connected to a check valve 22 which -isinA turn connected to a conduitr 24 leading to an accu.-V

mulator 26; Branching to the left from conduit 24 is a pressure conduit26 leading to a pilot valve unit 3|).A Branching Afrom conduit 24to theright is a conduit 32 leading to-any actuated hydraulic devices. Leadingfrom pilot valve 30 is a conduit y34 connected to the bottom of valvehousing' I8. Also leading from pilot valve 30 the rpoppetv valveelement46, and'exhaust `conduit I9 'connects with recess 4I ata pointvbelow the poppet valve element v46. Conduit34 isv connected to therecess at a point below the'piston 42.

When the hydraulic system of Figure 1V be' ing operated, the pump I4takesiiuid from reservoir I0 and pumpsit through conduits I6 and 20 andcheck valve-22 into the accumulator 26.

Hydraulic devices connected to conduit 32w con? sume'I this nuid undervpressurewhen they are iactuated. If hydraulic duid is not consumed atthe rate at which the pump-|4 deliversit, the pressure will build up inthe accumulator.. until lit has reached the'point where it is necessaryor desirable to stop the build-up of pressure. At thispredeterminedpressure, the pilot valve is automatically operated. bythis fluid under pressure andcauses fluid to flow through confduit 34into valve` housing I8. This fluid acts `upon piston 42 to move itupwardly overcoming the pressure acting upon the poppet valve 46.

which is of -lesser area than the piston and opens the valve 46permitting the high pressure fluid from conduit I6 to be by-passed intoexhaust con- .duit I9 which will returnit to the reservoir I0.

. It hydraulic devices connected to conduit- 32 f are now operated thepressure in accumulator 1 Y 26 and consequently in theentlre hydraulicsystem .will drop to a. point to where vit isdesirable to build up thepressureagain. This drop in pressure will cause pilot valve-auto actautomatically to cut oil fluid flow into conduit 34 and zto.; connect.conduit -34 s to exhaust .conduit 38.

is a conduit 36 connected to exhaust conduit Isf` Valve housing I8 hasan axial recess at `4|) having a restricted portion 4I and an enlargedupper portion 43. Recess 40 retains a piston 42 having a stem 44leadingfrom the Vtopv thereof which abuts against a poppet valve element `46 furged downwardly upon the restriction 4I yforming its seat, by a coilspring 48. Pressure conduit I6 is connected with the recess 43 aboveThis action .causes Apressure to be Arelieved on the bottom ofpiston42.in-valve housing I6-allowing poppet I valve 46 tomclose. 'thus.stopping the by-pass of pressure iiuid to exhaust. vThus the pilotvalve 30 causes fluid pressure to be. bypassed` at4 the desired lhighpressurefandf stops the by-pass of pressure fluid at a lower desiredpressure.4 f'

The pilot valve element vention may be used for other purposes than thatdisclosed in `Figure 1, which is merely for purposes of illustration.Forfexamplaa pilot valve V element 30 could cause an electrical switchto be I v opened or'closed by suitable mechanism which switch might inturn 'control anelectric motor which may be themotive power rfor a pumpsuch as pump I4 inthe hydraulic system of Figure 1.

Thus the pilot valve 30 could control the supply of uuid to a hydraulicsystem directly, rather than y control "the by-pass of fluid underpressure from a plump which is continuously running. Various 30comprising this in-` 'other' uses for the pilot' valve are contemplatedby this invention and such uses as are mentioned are merelyillustrative.

The pilot valve 39 is shown in detail in Figure 2. A valve housing l hasan axial recess having an enlarged upper portion 52, a restrictedintermediate portion 54, an enlarged intermediate portion 56, and alarger lower portion 6I. A pressure inlet 60V is connected totheenlarged upper recessv 52, a cylinder` portv62 is connected to the 56 isan axially parallel passage 56 connected to inlet 66 at the 'top andconnectedto theen-l larged lower opening 56 at the bottorm'vand sealedby a plug 69 at the top.

Seated on the restriction between recess 52 and restricted intermediateportion and an exhaust; port 64 is connected to the enlargedintermediate' portion 56. Formed in the left part of housingk recess 54is a double poppet element having an 1 f `upper poppet 10 and alowerpoppet 12 andan upper guide stem 14. .s The double poppet is guidedby a closurecap 16 screwed into thel open ,end of recess 52 andcompressing `a spring ,16 down` wardly upon the double vpoppetelement..v Fitted lwithin the intermediate enlarged portion 56 is asealing ring 60 ofround cross section and a. bushing62 having holesthereinV to Vcommunicate the inside of the bushing withr the exhaustport 64. Fitted in bushing 62 is a stem 64 having an axialbore 66 initsupperend and .radial holes 96 communicating bore 66 with the outside.`Fitted on the bottom endof stem 64 is a washer 92, a number'ofBellevillek springs k94, and a. plastic pistoni 98 circumferentiallyrecessed to retain a sealing ring will An adjustment screw |02 passingthrough the bottom end-of piston 96 adjusts vthe distance betweenpistonl 96 and stem 64, and is held in place by a locknut |64. A cap 106seals theflower end` of recess 5l.

Referring to Figure 2,the pilot valve is operated by fiuid under-pressureentering port 60., fThe pressure istransmitted down passage 66t0 jact uponthe bottomof piston 66, forcing the piston and the stem.upwardly until the stem rcontacts the lower poppet 12 thus sealingcylinder port-62 off from the exhaustport 64. When the Y pressure buildsup further to overcome spring 94 and the seating pressure on poppet 10the poppet 10 is opened, permitting uid to pass into cylinder port 62`and thusactuate any desired device the operation Aof which is desiredto .be pressure responsive.

If the pressure delivered to port 69` should now drop, poppet valve 10would-seatthus cutting off flow of fluid to cylinderf62, trapping incylinder port 62 fluid under the: pressure at which the poppet 10closed. If the pressure should drop still further the spring 94" willforce the piston .allowing cylinder port62 to be connected to exhaustport 64. Any pressure responsive device operated by fluid-'from cylinderport 46,2 will now return to its original position.

From the operation thus far described, it is apparent that thedifferential between the'pressure required to close lowerv poppet I2Aand thev pressure required to open upper poppet 1li is a fixed quantitybuilt into the unit. AAs the pressure builds up, piston moves upwardlyagainst the spring 94 until lower valvel 12 is closed. Thereafter an'Aincrease inpressure has no effect upon the valve as aiwhole, until theincreased pressure on piston 96 isfgreat enough to overcome theuidpressure seating upper poppet l1li. cracking'of upper poppet 16 relievesthe. seating The first factors for opening the upper poppet 10.

pressure which results in anoverbalance of the opening pressure,snapping the valve 10 wide open, eliminating fluttering. It is apparentthat the pressure at which the lower valve 12 opens is dependent uponthe rate of the spring 94 and `the area of the piston 96. The openingpressure A10 will seat. A very minute additional lowering of thepressure will cause lower poppet 12 to open,

causing th'e power valve I6 to return to its normal closed position.From the foregoing it will be apparent that the upper poppet 19 does notseat at the same pressure at which it opens, but rather ata lowerpressure than the seating pressure by an amount represented by the meaneffective pressure overthe cross-sectional seating area of theupperpoppet 10, This pressure obviously is the initialY pressure Iatwhichv thelower DOPDet 12v closed when theV pressure of the system wasincreasing. y v

If it is desired to increase the differential pressure between theeffective pressures atwhich upper poppet 10 opens and closes, whichdif'- .ferential is equivalent to the differential at which lowerpoppet12 closesrelative to that vat which upper Vpoppet .10 opens, this may bedone by adding the-rate of the spring to the determining A poppetarrangement to accomplish this purpose is shown in Figure 3, wherein alowerrpoppet 12 is connected to an upper poppet 10' with a lost- `motionconnection. The lost-motion connection is provided by forming 'upperpoppet 10 with a threaded Vhole 1I in the bottom intofwhich is screwed athreaded bushing 13. The bushing 13 retains a threaded bolt 15 havingthe poppet 12 screwedv ony the bottom.H The bushing` 'I3 is screwed onlypart way into the hole 1l to allow kbolt15 to slide freely in thebushing. i

' 96 downwardly until the lower poppet 12 unseats 1 The operation ofthevalves of Figure 3 is as follows: As the pressureI builds up valve 12closes. Due to the Vlost-motion connection, however, additionalpressurev acts upon the spring k94 `(Figure 2) forcing poppet 12'upwardly until bolt 15'contacts upper poppet 10'. This lost motion isaccomplished, however, only by overcoming the increasing resistance ofthe spring 94, whicheffectively adds to the differential pressures the lrate vof that spring. After the bolt 15 Vcontacts .upper poppet 10?there 4must be an additional b uiId-upin pressure suflcient toovercornethe seating pressures on poppet 10' before that poppet `willopen. When this point is reached poppet 10' snaps opensimilarly topoppet/1li of Figure 2.

When the pressure recedes, p0ppet1ii' willseat at the pressure at whichlower poppet abuts upon the upper poppet 10' when the `pressure isinicreasing. A further decrease in pressure, however, will notopenpoppet 12 because of the lostmotion connection. kWhen the pressuredecreases inamounts Vto where the spring 94 forces the stem 84downwardly until it unseats poppet 12', the

. trapped fluid in cylinder port 62 will be released and the power valveof Figure 1 will return to its .nor-mal closed. position.A f Itistherefore apparent that the provision of a lost motion between the vat a minimum to cut down on weight.

two poppets l' and 'l2'y effectively increases the differential pressureat which the pilot opens .and closes dependent upon the amount of lostmotion allowed to the poppet 12.

This adjustment is useful in adapting the function of the present valveto various pressure differential requirements. There are various toppressures desirable foi-,different hydraulic systems and consequentlydifferential pressures. The pilot valve is adjusted to the top pressuresby changing the rate of spring 94 by adding more spring units. Thedifferential is adjusted by positioning bushing 13 within upper poppet'I0'. 'Ihus the present valve can meet a large variety of pressurerequirements with but simple changes and adjustments.

The pilot valve 30 is superior to slide valves or cylinder valves suchas are commonly usedl in regulators because it will not leak. Inpresentday hydraulic systems such as those used on aircraft the amountof hydraulic fluid must be held Thus any regulator which leaks a smallamount, for

example a few drops a minute, is unsatisfactory because the pressureregulator for the system will be intermittently operated at frequentintervals lessening its life. The present pilot valve is free fromleakage because poppet valves are used in which leakage can be'reducedto zero through proper construction. Although piston operated poppetvalves have been used in the past, the present pilot valve providesmeans to direct iluid pressure to a power device and to return the uidto exhaust after operating the power device, thereby returning the powerdevice and the stem 84 to its original position. The piston 9B can bemade free from leakage as compared to a slide valve because a seal canbe used whereas it is impossible to use a seal on a slide valve.

The pressure at which the upper poppet 10 can be made to open and closeand the pressure at which the bottom poppet 12 may be made to open andclose is regulated by the rate of the spring 94. In this regard aBelleville spring is highly desirable in that additional discs may beadded to give a longer spring and thus a different rate. Minuteadjustments as to pressure are handled by the adjustment screw |02. Thepilot valves therefore can be made to lit any desired operatingpressures by very simple adjustments.

The valve 3i) is also inexpensive to manufacture because of the co-axialalignment of all recesses and movable parts. Thus boring operations arepossible witha minimum of set-ups, reducing manufacturing costs.

Although this invention has been described with reference to aparticular embodiment thereof, it is not limited to this embodiment norotherwise except by terms of the following claims.

1. In a pilot valve, a valve housing having a pressure port, a cylinderport, an exhaust port, and a bore connecting said ports and having avalve seat formed therein between said pressure port and said cylinderport, a rst poppet valve adapted to seat on said valve seat and sealingsaid pressure port from said cylinder port, a second pGppet valvesealing said cylinder port from said exhaust port, said second poppethavlng a lost-motion connection with said first popable axial positionwith regard thereto, and pressure responsive means governing theposition of said .second poppet valve seat and acting through saidsecond poppet to open said rst poppet.

2. In a valve, a housing having connecting small and large bores andanenlarged chamber at the outer end of the small" bore forming a valveseat, said housing having a pressure port communicating with saidchamber and with the outer end of the large bore, said housing having acylinder port connecting to said small bore, said housing having anexhaust port connecting with at least one of said bores at a pointtoward the large bore with' respect to said cylinder l port, a piston insaid large bore, a stem in said small bore connected to said piston andhaving a passage therein from the end remote from the piston to a regionnear the exhaust port, said passage forming a valve seat on said remoteend of saidL stem, resilient means resisting movement of the pistontoward the small. bore, a poppet seated on said seat formedjby thepassage in said stem, and a second poppet seated on the seat formed atend of the small bore, sealing said :bore from the pressure port, theeffective pressure seating area of said valve seat on said small borebeingl at least as large as thercross sectional area of the stem.

3. In a valve, a housing having coaxial connecting large and smallcylindrical bores with an enlarged chamber at the outer end of the smallbore forming a valve seat at the bore. said housing having a pressure-port communicating with the outer end ,of the large bore, and saidchamber, said housing having a cylinder port connecting withthe smallbore and having an exhaust port connecting with at least one of saidbores ata point near their junction, a piston in said large bore, a stemconnected to said piston in said small bore and having a passage fromthe outer end toward an intermediate point adjacent to the exhaustopening said passage formings a valve seat at the outer end of the stem,resilient means resisting movement of said piston toward said smallbore,a first poppet seated on said valve seat at the outer end of the smallbore to seal the same from the pressure port, and a second poppet seatedon said valve seat on said stem covering said passage and having anadjustable lost motion connection with said rst PODDE- 4. A valvecomprising bore and, in axial sequence, a pressure port, a cylinderport, and an exhaust port, all communicating with said main bore; aIlrst valve seat means in said main bore between said pressure port andsaid cylinder port; a rst poppet adapted to seat on said first valveseat; movablev means in said bore betweensaid cylinder port and saidexhaust port forming a second valve seat; a second poppet adapted toseat on said second valve seat and to lift said rst poppet f* andpressure responsive means to move said movpet, a seat for said secondpoppet having a vari! a housing having a main'

